linux-cve-announce - CVE-2025-71159: btrfs: fix use-after-free warning in btrfs_get_or_create_delayed

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Message-ID: <2026012346-CVE-2025-71159-417a@gregkh>
Date: Fri, 23 Jan 2026 16:24:46 +0100
From: Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To: linux-cve-announce@...r.kernel.org
Cc: Greg Kroah-Hartman <gregkh@...nel.org>
Subject: CVE-2025-71159: btrfs: fix use-after-free warning in btrfs_get_or_create_delayed_node()

From: Greg Kroah-Hartman <gregkh@...nel.org>

Description
===========

In the Linux kernel, the following vulnerability has been resolved:

btrfs: fix use-after-free warning in btrfs_get_or_create_delayed_node()

Previously, btrfs_get_or_create_delayed_node() set the delayed_node's
refcount before acquiring the root->delayed_nodes lock.
Commit e8513c012de7 ("btrfs: implement ref_tracker for delayed_nodes")
moved refcount_set inside the critical section, which means there is
no longer a memory barrier between setting the refcount and setting
btrfs_inode->delayed_node.

Without that barrier, the stores to node->refs and
btrfs_inode->delayed_node may become visible out of order. Another
thread can then read btrfs_inode->delayed_node and attempt to
increment a refcount that hasn't been set yet, leading to a
refcounting bug and a use-after-free warning.

The fix is to move refcount_set back to where it was to take
advantage of the implicit memory barrier provided by lock
acquisition.

Because the allocations now happen outside of the lock's critical
section, they can use GFP_NOFS instead of GFP_ATOMIC.

The Linux kernel CVE team has assigned CVE-2025-71159 to this issue.

Affected and fixed versions
===========================

	Issue introduced in 6.18 with commit e8513c012de75fd65e2df5499572bc6ef3f6e409 and fixed in 6.18.6 with commit c8385851a5435f4006281828d428e5d0b0bbf8af
	Issue introduced in 6.18 with commit e8513c012de75fd65e2df5499572bc6ef3f6e409 and fixed in 6.19-rc5 with commit 83f59076a1ae6f5c6845d6f7ed3a1a373d883684

Please see https://www.kernel.org for a full list of currently supported
kernel versions by the kernel community.

Unaffected versions might change over time as fixes are backported to
older supported kernel versions.  The official CVE entry at
	https://cve.org/CVERecord/?id=CVE-2025-71159
will be updated if fixes are backported, please check that for the most
up to date information about this issue.

Affected files
==============

The file(s) affected by this issue are:
	fs/btrfs/delayed-inode.c

Mitigation
==========

The Linux kernel CVE team recommends that you update to the latest
stable kernel version for this, and many other bugfixes.  Individual
changes are never tested alone, but rather are part of a larger kernel
release.  Cherry-picking individual commits is not recommended or
supported by the Linux kernel community at all.  If however, updating to
the latest release is impossible, the individual changes to resolve this
issue can be found at these commits:
	https://git.kernel.org/stable/c/c8385851a5435f4006281828d428e5d0b0bbf8af
	https://git.kernel.org/stable/c/83f59076a1ae6f5c6845d6f7ed3a1a373d883684